Use of Highly Hydrophobic Ionic Liquids for Ion-selective Electrodes of the Liquid Membrane Type

Abstract

The phase-boundary potential at the interface between an aqueous KCl solution (W) and a hydrophobic room-temperature ionic liquid (RTIL), trioctylmethylammonium bis(nonafluorobutylsulfonyl)imide ([TOMA(+)][C(4)C(4)N(-)]), containing dicyclohexano-18-crown-6 (DCH18C6), shows the nernstian response to K(+) in W within a polarized potential window of 500 mV between [TOMA(+)][C(4)C(4)N(-)] and W, demonstrating that hydrophobic RTILs can be used as a nonvolatile ionic medium for liquid-membrane ion-selective electrodes. The complex formation constant of K(+) with DCH18C6 in [TOMA(+)][C(4)C(4)N(-)] is estimated to be on the order of 10(9) from the upper detection limit using a partition equilibrium model in the presence of a neutral ionophore. The response time of the phase-boundary potential is approximately 20 min. Gelled [TOMA(+)][C(4)C(4)N(-)] also shows the nernstian response to K(+), although the upper limit is lower probably due to a change in the solvent properties from the non-gelled [TOMA(+)][C(4)C(4)N(-)]. The response time of the gelled [TOMA(+)][C(4)C(4)N(-)] is approximately 5 min, shorter than that of the non-gelled [TOMA(+)][C(4)C(4)N(-)].